The present invention provides an efficient and cost-effective solution for two serious ecological problems. The first problem is water and earth pollution due to the accidental and inevitable operational spills of oil products. The second one is the accumulation of waste rubber tires. Using the below-referenced multi-directional method of waste tire rubber de-vulcanization process, a product has been identified exhibiting a high degree of sorbing of oil product.
Throughout this patent application the term “sorb” or “sorbing” is used to encompass both absorption and/or adsorption. Although absorption and absorbability are this not synonymous with sorbing and ability to sorb, the term “absorbability” and “absorption” as used in the tables are used to indicate ability to sorb.
The methods of manufacturing oil product absorbents from secondary rubber are well-known. U.S. Pat. No. 3,567,660 proposes to use crushed rubber of waste tires. The absorption of oil products occurs due to swelling of rubber. However, swelling of vulcanized rubber with a dense molecular space grid is known to be insignificant. This factor has been taken into account by U.S. Pat. No. 4,039,489, which suggests specially synthesizing a polymer with the minimum number of lateral bonds in order to maximize the polymer swelling capability. The obvious drawback of this method is its inefficiency, because it requires a new polymer material to be synthesized instead of making use of abundant secondary raw material. In addition, the ecological problem associated with the accumulation of waste tires would also still remain unsolved.
The degree of oil product absorption is determined not only by the swelling capability of the material since the swelling capability is itself determined by the structure of the material. In the process of collecting the oil, the material of the absorbent acts as a system of particles linked together, rather than the system of isolated particles. Therefore, the role of structures formed by these particles, i.e., that of agglomerates, is no less, and maybe, more, important. In this situation, first of all, the selective capillary effect becomes apparent. The liquid wetting the walls of capillary (in our case, oil or any petroleum based product) enters the space between the particles, whereas the non-wetting liquid (in our case, water) does not enter such space.
Technical solutions to creating an effective srobents from waste rubber using the selective capillary absorption of oil products, e.g., U.S. Pat. No. 5,180,704, are well known. To increase the inter-particle adhesion, the authors propose to modify a part of the rubber crumb surface by means of de-vulcanization. As a result, the particles adhered to one another form a capillary system. The selective capillary mechanism is proposed in a number of other works, e.g., U.S. Pat. Nos. 4,039,489, 5,972,470, 6,110,863, where a wide variety of powder- and fiber-like materials of different origin, including fibrous polypropylene and industrial wastes, are used as sorbents.
All of these methods have proved to be insufficiently effective due to drawbacks inherent to the capillary mechanism of absorption. First, the capillary effect strongly depends on the viscosity of product being absorbed, which, in turn, depends on the ambient temperature. On the surface of large water basins, where oil spills take place, the temperature is relatively low; therefore, the product viscosity increases, and the rate of absorption decreases. Second, when removing the bulk of sorbent along with the absorbed oil from water, the capillary structure is disrupted, and ceases to hold oil products.
Thus, the oil sorbing process can be implemented by different mechanisms at different levels: (a) swelling determined by the macromolecular structure (chain length) and cross-linking of macromolecules (vulcanization grid); (b) surface absorption, which depends on surface branching, in particular, on the size of particles; and (c) capillary absorption at the level of material particle system determined by the particle set structure. In sum, the particulate material used for oil absorption achieves the absorption by allowing the oil products to be absorbed inside the particles, on the surface of the particles, and in the interstitial spaces between particles.
Therefore, there is compelling need to try to create a system, which could make use of all three oil product collection mechanisms simultaneously. Waste rubber crumb conglomerations, as described in the above-mentioned patents, fully enable only two of the three mechanisms, namely those of surface absorption and capillary absorption. Conceptually, the third mechanism, swelling, can be enabled by rubber de-vulcanization.
The known methods of waste tire rubber de-vulcanization are described, e.g., in European Patent no. EP 0690091 to Sekhar et al. The drawback of this method consists, first of all, in that it gives a paste-like output product due to the use of liquid, plastic, and/or softening substances like diols, stearic acid, natural rubber, etc. as modifying de-vulcanization agent components. The product having this physical form cannot be dispersed over the surface of the water, earth, etc. Therefore, a requirement for the waste rubber processing technology is that it provide a definite physical consistency of the product in order to be suitable for use in oil product absorption.
Another known rubber de-vulcanization method is that described in U.S. Pat. No. 6,541,526. In the technology described in this patent, a powder-like modifier is used for the de-vulcanization of secondary rubber. Disintegrated rubber is subjected to thermomechanical treatment in roll mills in the presence of modifier. The final product of this process, completely de-vulcanized rubber, also does not meet the above-described physical consistency requirement for an effective sorbent.
As indicated, there is a compelling need to develop a method of manufacturing an efficient oil product sorbent that can fully and successfully make use of all three oil absorption mechanisms: namely, swelling, surface absorption, and capillary absorption. Ideally, such a method should also be capable of solving a pressing ecological problem, the accumulation of waste rubber from rubber tires, by using waste rubber from the accumulated rubber tires as its raw material.